Connected: An Internet Encyclopedia
RFC 1323 - APPENDIX C: CHANGES FROM RFC-1072, RFC-1185

Top: Connected: An Internet Encyclopedia
Up: Requests For Comments
Up: RFC 1323
Prev: B.2 Closing and Reopening a Connection
Next: APPENDIX D: SUMMARY OF NOTATION

### APPENDIX C: CHANGES FROM RFC-1072, RFC-1185

The protocol extensions defined in this document differ in several important ways from those defined in RFC-1072 and RFC-1185.

1. SACK has been deferred to a later memo.

2. The detailed rules for sending timestamp replies (see Section 3.4) differ in important ways. The earlier rules could result in an under-estimate of the RTT in certain cases (packets dropped or out of order).

3. The same value TS.Recent is now shared by the two distinct mechanisms RTTM and PAWS. This simplification became possible because of change (2).

4. An ambiguity in RFC-1185 was resolved in favor of putting timestamps on ACK as well as data segments. This supports the symmetry of the underlying TCP protocol.

5. The echo and echo reply options of RFC-1072 were combined into a single Timestamps option, to reflect the symmetry and to simplify processing.

6. The problem of outdated timestamps on long-idle connections, discussed in Section 4.2.2, was realized and resolved.

7. RFC-1185 recommended that header prediction take precedence over the timestamp check. Based upon some scepticism about the probabilistic arguments given in Section 4.2.4, it was decided to recommend that the timestamp check be performed first.

8. The spec was modified so that the extended options will be sent on <SYN,ACK> segments only when they are received in the corresponding <SYN> segments. This provides the most conservative possible conditions for interoperation with implementations without the extensions.

In addition to these substantive changes, the present RFC attempts to specify the algorithms unambiguously by presenting modifications to the Event Processing rules of RFC-793; see Appendix E.

Next: APPENDIX D: SUMMARY OF NOTATION

Connected: An Internet Encyclopedia
RFC 1323 - APPENDIX C: CHANGES FROM RFC-1072, RFC-1185